1. Field of the Invention
The invention relates to a tracking error detecting circuit of a magnetic recording and reproducing apparatus in which pilot signals to detect a tracking error are recorded together with a main signal onto a magnetic recording medium and, upon reproduction, the tracking error is detected from reproduction output levels of the pilot signals.
2. Description of the Related Art
Hitherto, in a tracking error detecting circuit which is used in an 8 mm video tape recorder, four low frequency pilot signals of different frequencies are set and the low frequency pilot signals are frequency multiplexed one by one to a video signal and recorded every video track.
Upon reproduction, two low frequency pilot signals recorded on both of the adjacent video tracks are detected as a crosstalk from the adjacent video tracks and reproduction output levels of two low frequency pilot signals are compared, thereby detecting a tracking error (for instance, Akira Hirota, "WITH RESPECT TO THE 8 mm VIDEO TAPE RECORDER (1)" Technical Report of Japan Society of Television, VR61-1, Published on Feb. 23, 1984).
FIG. 16 is a block diagram showing a construction of a tracking error detecting circuit which is used in the conventional 8 mm video tape recorder (VTR).
In FIG. 16, a signal recorded on a magnetic recording medium 501 is reproduced by a magnetic head 502 and an amplifying circuit 503. The reproduced signal includes pilot signals from both of the adjacent tracks. A 4-frequency generating circuit 504 generates a signal having the same time base and frequency as those of the pilot signal of the reproduction track by using a clock generated from a color APC (Auto Phase Control) of the 8 mm VTR and a PG (rotating position detection pulse) of the 8 mm VTR. The signal from the generating circuit 504 is multiplied with the pilot signals from both of the adjacent tracks by multiplying circuits 505 and 506.
The signals generated from the multiplying circuits 505 and 506, therefore, include a signal having the same frequency as that of a horizontal sync signal and a signal having a frequency which is three times as high as the frequency of the horizontal sync signal due to the pilot signals from both of the adjacent tracks in which time base fluctuation errors have been corrected.
A signal having the same frequency as that of the horizontal sync signal and a signal having the frequency which is three times as high as the horizontal sync frequency are extracted by band pass filters (hereinafter, abbreviated to BPFs) 507 and 508.
Detecting circuits 509 and 510 execute the square detection or full wave detection and detect amplitude values of the signals generated from the BPFs 507 and 508, respectively. Unnecessary components are eliminated by low pass filters (hereinafter, abbreviated to LPFs) 511 and 512. A difference between outputs of the LPFs 511 and 512 is obtained by a subtracting circuit 513, thereby detecting a tracking error signal.
However, hitherto, in the case where the tracking error detecting circuit is further made correspond to a format which needs to realize a narrow track or the like, it is necessary to further set the band of the BPF to a narrow band in order to improve the detecting accuracy of the tracking error.
Even when a tank circuit of a narrow band (high Q) is used for the BPF, however, a range of up to Q=20 can be realized and it is difficult to realize a hardware which provides a value of Q higher than such a value.
Even in the case where a digital signal is used as a main signal and recorded together with the pilot signals for tracking or the like, since the digital signal has a signal component until the low frequency band, a recording/reproduction C/N ratio of the pilot signal deteriorates. To compensate the deteriorated amount, the band of the BPF also similarly needs to be made narrow and a problem similar to that mentioned above occurs.